1. Field of the Invention
The present invention relates to a method and a program for correcting a peak position as preprocessing for testing of whether a product, etc., is good or defective from a spectrum waveform pattern thereof.
2. Description of the Related Art
There exist a lot of products and materials capable of using a spectrum waveform for testing of whether the product is a good one or a defective one. For example, as shown in FIGS. 7A and 7B, a fluorescent tube has different energy intensities depending on wavelength so that the emission property can be expressed by the spectrum waveform. The properties of herb medicine materials, agricultural products, and petrochemical products can also be expressed as spectrum waveforms by using a chromatograph or an infrared spectrometer, as shown in FIG. 8.
In this manner, in the industry field or in the fields of chemicals, agriculture, etc., the spectrum waveform is widely used for testing of properties of products and raw materials/ingredients. In every field, the spectrum waveform of a product to be tested is compared with the spectrum waveform group that was judged as a good product in the past to judge whether it can be regarded as the same. For example, supposing the waveform shown in FIG. 7A is a typical spectrum judged as a good product in the past, the same waveform pattern is regarded to appear in substantially every portions in FIG. 7B. However, the mountain figure of the wave pattern indicated by the arrow of FIG. 7A has a difference from the wave pattern of FIG. 7B, thus generating question about identities of spectrum waveforms.
At the same time, there exist substantively no just the same spectrum waveforms. More specifically, there exist no same spectrum waveforms which are completely coincident with each other both in the vertical axis direction and horizontal axis direction. Differences are present among individuals even in good products. A completely coincident waveform pattern cannot be acquired even when the same object is measured by the same measuring equipment. One reason is the presence of various errors such as an error among individuals to be measured, a variance in the properties of the object itself, and a measurement error inherent to the measuring equipment. These errors occurs in both directions of the vertical axis and horizontal axis.
As described above, although there exist no just the same spectrum waveforms, testing of products by use of a spectrum waveform, that is, judgment of degree of similarity of spectrum waveforms is carried out. Thus, an error especially in the horizontal axis direction often becomes problematic in the testing process. The reason is that, when comparing the spectrum waveforms, if peaks and irregularity positions are level in the horizontal axis direction, the testing can easily be performed by focusing on only the difference in the vertical axis direction.
A measurement result by chromatograph is one example of easy occurrence of errors of the spectrum waveform in the horizontal axis direction. The chromatograph easily causes an error in the horizontal axis direction due to its measurement principle so that when the same testing object is measured more than once, the same peak in the horizontal axis direction may appear in the range of several percentages of the whole horizontal width of the spectrum waveform. Therefore, as for the peak position correction especially for the chromatograph, studies using a statistical approach and the like have been carried out. In the other spectrum waveforms, even though there is some difference, occurrence of an error is inevitable. Accordingly, peak position correction has become an important problem in the visual testing or computer-based automatic testing since the error highly affects the testing accuracy.
An example of a peak position error of a spectrum waveform is shown in FIG. 5B. FIG. 5B shows three different object spectrum waveforms having the same properties. In the diagram, positions of “peak A”, “peak B”, and “peak C” which express properties of materials are different in the horizontal axis direction. The difference may be caused by errors owing to the above various parameters. These three different spectrum waveforms have nonlinear errors in the horizontal axis direction. More specifically, the error does not occur in the form of mere translation or even expansion and contraction in the horizontal axis direction, but nonuniformly fluctuates depending on the place.
Consequently, it is highly required as preprocessing of the testing to perform the error correction in the horizontal axis direction, i.e., peak position correction with high accuracy (in other words, to match as much as possible the positions in the horizontal axis direction of fellow peaks to be regarded as the same peak as for a plurality of peak positions of the spectrum waveform). In addition, the peak position correction must be performed not only in high accuracy but also as rapidly as possible. Especially recently, a development for performing the test processing with a computer has been advanced and a development of an elemental technology to be required has been performed (for example, see the method described in commonly assigned Japanese Patent Application Laid-Open Publication No. 2004-110602 according to development by the inventor). When testing process is performed by a computer, a peak position correcting method becomes essential in particular. The reason is that peaks can flexibly be associated in case of visual checks, but that judging the accuracy would extremely deteriorate if the corresponding peaks are not properly specified in case of computers.
Hitherto-applied typical methods of the peak position correction are as follows.
(1) A method of selecting one typical peak from a spectrum waveform and adjusting another spectrum to the selected typical peak in the horizontal axis position (see FIG. 9A).
This method is effectively applied when the spectrum waveform uniformly shifts in the horizontal axis direction. The more the selected typical peak is positioned in substantially center of the spectrum waveform in the horizontal axis direction, the more error correction at both ends may fairly be performed.
(2) A method of preparing a sample having one or a plurality of ingredients whose peak appearance positions in the horizontal axis direction are known, measuring the sample, and correcting the corresponding peak positions appearing in the testing object relative to the appearing peeks (see FIG. 9B).
The two vertical lines described in FIG. 9B designate the peak appearance positions of the known ingredients. When two ingredients are used, corresponding peaks of the spectrum waveform to be tested are adjusted to the two peak positions and the waveform therebetween is expanded or contracted in a linear processing manner. The method of using peak appearance position of the known ingredient is a method generally used in a chromatograph, etc., and is called “internal standard”. Error in the horizontal axis direction of spectrum waveform generally involves expansion and contraction, so that using two peaks provides better effect in peak position correction.
(3) A method of selecting two typical peaks from among peaks of a spectrum waveform defined as a standard and correcting the corresponding peaks of another spectrum waveform at the typical peak positions (see FIG. 10).
In the example shown in FIG. 10, the right and left two peaks are selected and the spectrum waveform existing between the peaks is expanded or contracted in a linear processing manner. In general, by selecting peaks nearer to both ends as far as possible, correction effectiveness may be improved. The method is, for example, described in the specification of U.S. Pat. No. 5,969,228. A different point from the above described internal standard method is no need for separately preparing samples.
In the above methods (1) and (2), however, the number of peaks set or selected as a correcting standard are about two and a peak position existing between the peaks is merely expanded or contracted in the proportional manner to be corrected. That is, there exists a problem in that the methods are unavailable for a spectrum waveform which is expanded or contracted in a nonlinear manner though available for a spectrum waveform which is expanded or contracted in the proportional manner.
Particularly, in a chromatograph, etc., peak appearance positions are fluctuated in a nonlinear manner. For example, a peak may shift to the front and another peak may shift to the rear. In this case, the conventional methods involve problems in that correcting accuracy of peak position except correction reference peak may become extremely insufficient and that error of peak position may rather increase by the correction.